Hydromechanical lost motion servo valve



Feb. 20, 1958 c. c. EHLKE ETAL 3,369,460

HYDROMECHANICAL LOST MOTION SERVO VALVE Filed April 15, 1966 j 4 Z w 3 2INVENTORS (HA/MES 6. E HLKE DONALD K STROHSCHE/N .JOHN W. VA NC EYUnited States Patent Cfiiice 3,369,463 Patented Feb. 20, 1968 3,369,460HYDROMECHANICAL LOST MOTION SERVO VALVE Charles C. Ehlke and Donald K.Strohschein, Naperville,

and John W. Yancey, East Peoria, Ill., assignors to Caterpillar TractorCo., Peoria, Ill., a corporation of California Continuation-impart ofapplication Ser. No. 363,241,

Apr. 28, 1964. This application Apr. 15, 1966, Ser.

3 Claims. (Cl. 91-49) This application is a continuation-in-part of ourassignees U.S. Ser. No. 363,241, now Patent No. 3,262,525, filed Apr.28, 1964.

The present invention relates generally to servo valves and moreparticularly to servo valves which accommo date lost motion in animproved and efficiently simple manner.

It is often required that mechanical movements be done in sequence. Forexample, in the steering of tracktype tractors by pedal actuatedcontrols in the manner described in the above-identified co-pendingapplication, it may be required that an engaged clutch becomesuccessively disengaged and thereafter that a brake be progressivelyapplied. If one movement, as for example the depression of one pedal, isto cause such a sequential two-step operation to take place in twoseparate mechanisms, such as in the clutch and in the brakes, it isusually required that lost motion be accommodated.

It is not unknown in the prior art to accommodate lost motion. A commonway of accommodating lost motion is by means of mechanical connections.Such mechanical connections may take the form of a mechanicalpiston-cylinder arrangement wherein the piston may slide axially in atemporarily stationary cylinder until it contacts the head of thecylinder whereupon the piston and cylinder arrangement may then continuethe axial movement together.

Modern day earth moving equipment manufacturers tend to rely onhydraulically powered means and they also demand an economy of parts. Inview of these higher standards, the lost motion devices taught by theprior art'are unsatisfactory. In the present invention, the servo valvepiston is not only hydraulically actuated but it serves two functions,one of which is to provide the over-travel requirements of a lost motiondevice and the other is to act itself as an actuating member.

Accordingly, it is an object of the present invention to provide ahydromechanical servo valve which can accommodate lost motion.

It is a further object of the present invention to provide a servo valveadapted to permit over-travel between its hydraulically actuated pistonand a mechanically actuated control plunger.

It is a further object of the present invention to provide a servo valvehaving a hollow piston which not only accommodates lost motion but alsooperates as an actuating member.

It is yet another object of the present invention to provide ahydromechanical lost motion servo valve which senses wear in partsoperably associated with the valve.

Still further and more specific objects and advantages of the inventionand the manner in which the invention is carried into practice are madeapparent in the following secification wherein reference is made to theaccompanying drawing.

In the drawing:

FIG. 1 is an enlarged sectional view of one embodiment of thehydromechanical servo valve of the present invention;

FIG. 2 is a view like FIG. 1 illustrating the piston of the servo valvein its position of maximum displacement; and

FIG. 3 is an enlarged sectional view of an alternate embodiment of theservo valve of the present invention.

Referring to FIGS. 1 and 2, an embodiment of the hydromechanical servovalve 10 of the present invention is shown fixedly supported between arotatable shaft 11 and a manually operable lever 12. The shaft carriesat its upper end .a lever 13, one end of which is bifurcated topivotally mount an anti-friction roller 14 between its bifurcated ends.The lever 12 pivotally supports an antifriction roller 15 at its lowerend.

The servo valve has a housing 16 which is internally, concentricallybored to form cylindrical surfaces 17 and 18 which respectively receivefor reciprocal movement therein, an hydraulically operable hollow piston19 and a mechanically activated control plunger 20. The hollow pistonhas an internal bore 21 in which the forward end of the plunger may beslidably received. The piston has another internal bore 22 which isconcentric with bore 21 but which is of slightly greater diameter. Theside walls of the piston have surface ports 23 which communicate withaxial passageways 24 also in the side walls. These axial passagewaysopen to the rear of the piston. The forward end of the hollow piston haschamfered edges and diverging passageways 25, which provide access fromthe internal bore 22 of the piston to the atmosphere.

The rear end of the housing terminates in a shoulder 26 which serves asa seat for one end of a compression spring 27. The other end of thespring engages a seat 28 attached to the rear end of the plunger. Thespring urges the plunger rearwardly .and against any forward axialthrust which may be imparted to it by lever 12.

The forward, piston-engaging end of the plunger has a pair of transverseand interconnected passageways 30 which communicate with axial bore 31itself opening to the forward end of the plunger.

Between bores 17 and 18 of the valve housing is a bore 32 which is ofrelatively small axial extent and which has an internal diameterslightly larger than bore 17.

Oil under pressure from a source, not shown, enters bore 32 from a port33 shown in FIG. 1. In the position that the forward end of the plungerassumes with respect to bore 21 of the piston in FIG. 1, the oil flowsfrom port 33 to the atmosphere and a reservoir (not shown) viaintermediate bore 32, transverse passageways 30, axial bore 31, bore 22of the hollow piston and diverging passageways 25.

In operation, when it is desired to rotate shaft 11, lever 12 ismanipulated clockwise causing it to apply a forward axial thrust at therear end of the plunger. If the plunger is advanced sufficiently toblock transverse passageways 30 in its forward end, the oil will betemporarily trapped in intermediate bore 32 causing an oil pressure tobuild up behind the rear end walls of the piston. This pressure willcause the piston to advance forwardly and will cause shaft 11 to rock.Further forward movement of the plunger will similarly cause the pistonto advance further. Hence, the shaft will rock in proportion with themovement of lever 12. In view of the radial passageways 30 and the axialbore 31 at the end of the plunger, successive forward and backwardmovements of the plunger so as to open and close fluid communicationbetween ort 33 and the interior chamber or bore 22 of the piston willserve to modulate the fluid pressure in bore 32 and will modulate themovement of the piston.

It is significant to note that the oil pressure acts only to advance thepiston and that it does not react against the forward end of the plungerso as to push the plunger rearwardly. Accordingly, the force that isrequired to advance the plunger is only that force which will overcomethe counteracting force of spring 27. Also it is significant to notethat although the piston is advanced hydraulically and independently ofthe plunger, the relative position of the advancing piston with respectto bore 17, can be gauged by the relative displacement of the plunger.

Referring to FIG. 2 the piston is shown in its position of maximumdisplacement. In this position the surface ports 23 have becomepartially uncovered and they extend beyond the forward end of the valvehousing. This allows the oil emanating from port 33 to flow toatmosphere as shown by the arrows via the axial passageways 24 and thesurface ports in the piston. In the position shown in FIG. 2 the pistonis in a balanced condition. The hydraulic pressure force acting againstthe rear end of the piston is counterbalanced by the restoring force ofthe spring-loaded mechanism (not shown) operably associated with shaft11. It will be recognized that in FIG. 2 the venting of the oil toatmosphere via surface ports 23 will not relieve all the pressure acting.against the rear end of the piston. The final pressure acting againstthe rear end of the piston will depend primarily on the pressure of theoil emanating from port 33 and the amount that the surface ports areuncovered and extend beyond the end of the housing.

Without affecting the piston in its position of FIG. 2,

plunger may yet be advanced relative to the interior of the hollowpiston to the position shown in phantom lines in FIG. 2. Therefore, iflever 12 is adapted to activate another member in addition to theplunger, this overtravel feature of the valve permits the sequentialoperation of such other member without affecting the piston in itsposition of maximum displacement.

It is not expected that in ordinary operations the forward end of theplunger will contact the forward end of the interior of the hollowpiston. However, the valve incorporates a notable safety feature in thatthe machine operator can advance the piston directly by such contact,and without relying on oil pressure, simply by manipulating lever 12with sudden and normally excessive force. Similarly the machine operatormay take advantage of this feature for displacement of the piston bypurely mechanical means should the oil pressure fall to an inoperativelylowcondition.

Referring now to FIG. 3, an alternate form of the piston, which iscapable of acting as a sensitive wear sensing device, is illustrated. Inthis embodiment of the invention, a thin flange 41 is formed on theforward end of the hollow piston and an angular groove 42 is formedimmediately behind the flange. Angularly divergent drain ports 43provide passageways between groove 42 and the reduced end 44 of theforward end of the interior of the hollow piston.

In the position of the piston shown in FIG. 3, the

effluent oil is slightly restricted by the walls of inner bore 17. Thisslight restriction causes .a small back pressure to be developed in theinterior of the hollow piston. The magnitude of this back pressure ismade evident to the machine operator by the magnitude of back pressurewhich is developed on the combined reaction surfaces of thecircumferential portion 45 of the forward end of the plunger and of theback wall 46 at the end of axial bore 31. If a member, such as a springloaded clutch (not shown), is operably associated withlever 13 suchthat, when the clutch is worn, it returns the piston to the positionshown in phantom lines of FIG. 3, then this embodiment of the inventionwill serve to warn the machine operator of the clutch wear. In thisposition of the piston, as shown in phantom lines, the oil restrictionand backup pressure caused by the walls of bore 17, flange 41 and groove42 are much greater. This increase in back pressure causes asignificantly large force of reaction to work against the forward end ofthe plunger. In result, the machine operator will realize a work loadsubstantially above normal in manipulating lever 12. This he mayinterpret as an indication that the clutch has worn.

We claim:

1. Ahydromechanical lost motion servo valve comprising, in combinationwith a source of fluid pressure and a reservoir therefor: a valvehousing having first and second concentric axial bores; a hollow pistondisposed for reciprocal movement in the first axial bore, and havingthird and fourth concentric axial bores, and also having first passagemeans in the head of the piston between atmosphere and the third axialbore, and also having second passage means in the side walls of thepiston between the rear surfaceof the piston and the surface of the sidewalls of the pistonat a point substantially at its mid portion; aplunger of uniform diameter disposed,

for reciprocal movement in the second axial bore of the housing and inthe third and fourth axial bores of the piston and havingsurface-opening, continuously interconnected axial and radial fluidpassageways in the forward end of the plunger; wherein, upon forwardaxial movement of the plunger to the extent that the radial fluidpassageways in the forward end thereof are blocked by the fourth axialbore of the piston, fluid entering the rear portion of the first borefrom a port adjacent the forward portion of the second bore causes thepiston to advance under hydraulic pressure.

2. The valve as defined in claim 1 further comprising resilient means'operably disposed between the rear end of the plunger and rear end ofthe valve housing for urging the plunger rearwardly.

3. The valve as defined in claim 1 wherein an annular portion of theside wallsof the piston adjacent the head thereof is relieved to providea reaction surface; and wherein the first passage means opens the thirdaxial bore of the piston to the relieved annular portion.

References Cited UNITED STATES PATENTS 1,259,883 3/1918 Lewis 9l4022,642,846 6/1953 Morgen 91-357 2,902,007 9/1959 Rockwell 91401 3,125,3193/1964 Arbogast et a1. 91-47 3,257,912 6/1966 Horst 91-49 MARTIN P.SCHWADRON, Primary Examiner.

EDGAR W. GEOHEGAN, Examiner.

a ADA S. tant E a

1. A HYDROMECHANICAL LOST MOTION SERVO VALVE COMPRISING, IN COMBINATIONWITH A SOURCE OF FLUID PRESSURE AND A RESERVOIR THEREFOR: A VALVEHOUSING HAVING FIRST AND SECOND CONCENTRIC AXIAL BORES; A HOLLOW PISTONDISPOSED FOR RECIPROCAL MOVEMENT IN THE FIRST AXIAL BORE, AND HAVINGTHIRD AND FOURTH CONCENTRIC AXIAL BORES, AND ALSO HAVING FIRST PASSAGEMEANS IN THE HEAD OF THE PISTON BETWEEN ATMOSPHERE AND THE THIRD AXIALBORE, AND ALSO HAVING SECOND PASSAGE MEANS IN THE SIDE WALLS OF THEPISTON BETWEEN THE REAR SURFACE OF THE PISTON AND THE SURFACE OF THESIDE WALLS OF THE PISTON AT A POINT SUBSTANTIALLY AT TIS MID PORTION; APLUNGER OF UNIFORM DIAMETER DISPOSED FOR RECIPROCAL MOVEMENT IN THESECOND AXIAL BORES OF THE HOUSING AND IN THE THIRD AND FOURTH AXIALBORES OF THE PISTON AND HAVING SURFACE-OPENING, CONTINUOUSLYINTERCONNECTED AXIAL AND RADIAL FLUID PASSAGEWAYS IN THE FORWARD END OFTHE PLUNGER; WHEREIN, UPON FORWARD AXAIL MOVEMENT OF THE PLUNGER TO THEEXTENT THAT THE RADIAL FLUID PASSAGEWAYS IN THE FORWARD END THEREOF THEBLOCKED BY THE FOURTH AXIAL BORE OF THE PISTON, FLUID ENTERING THE REARPORTION OF THE FIRST BORE FROM A PORT ADJACENT THE FORWARD PORTION OFTHE SECOND BORE CAUSES THE PISTON TO ADVANCE UNDER HYDRAULIC PRESSURE.